Breaker Doesn't Trip?

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anbm

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TX
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Designer
We have 400A thermal magnetic breaker to feed a 600A MLO panel, this panel feed (4) elevators at 70FLA (didn't know inrush current). We meter the panel and at certain time, the meter reads 850A at phase A and other time, it reads 1,200A at phase B. The 400A breaker never tripped. I am wondering why. Thanks!
 
anbm said:
We have 400A thermal magnetic breaker to feed a 600A MLO panel, this panel feed (4) elevators at 70FLA (didn't know inrush current). We meter the panel and at certain time, the meter reads 850A at phase A and other time, it reads 1,200A at phase B. The 400A breaker never tripped. I am wondering why. Thanks!
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How long are those currents present?

What is the breaker type (CAT#)?
 
Along with the great answers you have gotten I would ask how sure are you of your meter and it's settings? Is the meter set correctly for, or even compatible with the probe you are using?

Can you try it against a know load?

Can you look up the trip curves for the breaker you have?
 
According to the trip curve for a 400A Eaton-CH HKD breaker with fixed thermal trip, and adjustable magnetic trip, the lowest setting on the adjustable portion is 5x (5 x 400 = 2000A). The trip curve indicates that the 1200A would need to be present from between 60 secs-140 secs (error band)before the breaker would trip.

Your measurements were most likely catching the inrush from the motors due to elevator operation, and it was not the continuous amount of current.
 
If you had two elevators start at the same time, you would see probably around 840A (70 x 6 x 2); 3 at the same time would read 1260A. Do those values look familiar? :)
 
Jraef said:
If you had two elevators start at the same time, you would see probably around 840A (70 x 6 x 2); 3 at the same time would read 1260A. Do those values look familiar? :)
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Excellent deduction Dr. Evil. :grin:

I agree, looks like OP captured the inrush of one or more elevators starting.
 
Did anyone there key-up a two-way radio while you were taking the measurments?

I've seen that cause a current reading to show 1000-2000 amps while the load was really only a couple of hundred amps.

Steve
 
This happened only momentary, I agreed, this should be motor inrush current data.
 
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